As a flexible display which is bendable while displaying image information is developed, studies and developments are being conducted for a foldable type device in which a flexible display is applied to a device having two bodies and folding structures (for example, hinge units). In such a device, since the flexible display may be entirely disposed on two bodies via the folding structure so that a large size display may be implemented in the device.
As another device using the flexible display, a rollable type device in which a display has a winding structure is being studied and developed. In such a device, the flexible display is wound so that a size or an area of the entire display may be reduced and the flexible display is unwound so that the size or the area of the entire display may be increased.
In the foldable type device and the rollable type device, the flexible display is elastically deformed or elastically restored while changing the shape. Therefore, in a part of the flexible display which is deformed, spring back may be generated.
When the spring back of the flexible display is generated, interference or friction between the flexible display and the other part of the device may occur or the flexible display may be damaged or the operation of the device may not be smoothly performed. Therefore, it is necessary to consider to control the spring back of the flexible display.
In the device using the flexible display, the movement (for example, sliding) of the flexible display may be generated. In this case, when the smooth movement is not performed or uniform tensile force is not applied to the flexible display while being moved, it is difficult to operate the device and the flexible display may be irregular or damaged.
As a related art document using a flexible display, Korean Patent No. 1107127 (hereinafter, referred to as a related art 1) discloses a mobile terminal. The related art 1 includes a flexible display in which a size of a screen exposed to the outside is variable, a driving unit, a sliding member, a first rack gear, and a second rack gear.
In the related art 1, a pinion gear is engaged with the first rack gear and the second gear and when the pinion gear rotates by a motor which configures the driving unit, the flexible display moves in a longitudinal direction. However, the related art 1 does not specifically disclose how the driving unit and the motor are connected to the terminal body and how the driving unit and the motor are assembled with other configurations.
Therefore, when the terminal is formed by the related art 1, problems in that the pinion gear is not precisely engaged with the first rack gear and the second rack gear to be highly likely to be idle, the first rack gear and the second rack gear are slanted, the flexible display is not appropriately moved, or the flexible display is wrinkled are predictable.
Further, in the related art 1, the size of the screen of the flexible display varies by the driving of the driving unit, but a separate configuration which supports a bottom surface of the flexible display is not provided so that unevenness of the flexible display may be easily caused.
Further, in the related art 1, the first rack gear and the second rack gear are separated to be coupled to the pinion gear. However, backlash of the gear may cause the deflection of the flexible display during the operation and it is difficult to control an overall tension of the flexible display.
Further, in the related art 1, it is difficult to apply uniform tension to the flexible display and it is also difficult to control the spring back in a portion where the flexible display is deformed.
It is very important to form a slim mobile terminal with various functions to improve the merchantability of the terminal. However, in the case of the related art 1, the possibility of interference between the driving unit and various components in the terminal and the assembling structure of the driving unit cannot be considered so that it is difficult to expect the improvement of the merchantability.
As another related art document using a flexible display, Korean Patent No. 1695206 (hereinafter, referred to as a related art 2) discloses a screen extendable portable terminal. In the related art 2, the flexible display is rolled around a cylindrical rotation member equipped in the housing.
The related art 2 does not disclose a configuration which supports a bottom surface of the flexible display when the screen of the flexible display rolled around the cylindrical rotation member is extended so that the flexible display may be easily irregular or deflected.
Further, in the related art 2, it is difficult to apply uniform tension to the flexible display when the screen of the flexible display rolled around the cylindrical rotation member is extended or reduced so that an excessive load may be applied to the flexible display.
Further, it is difficult to apply a winding type flexible display to a relatively small-size portable device and a radius of curvature is deformed in a wound portion so that it may be difficult to control the entire deformation of the flexible display.
Further, the related art 1 and the related art 2 do not disclose a specific control method and unit when the screen of the flexible display is extended or reduced.